This invention relates to an amplifier, and more particularly to an amplifier having a function of muting, if necessary, signals sent forth from an output terminal.
An amplifier electrically amplifying a sound signal generally comprises a muting circuit provided with a field effect transistor (abbreviated as "FET") in order to attenuate signals produced from an amplifier output terminal without cutting off a power supply switch. This muting circuit is formed of the FET and a capacitor connected in series between an amplifier input terminal and a grounding terminal. The gate of the FET is connected to a terminal supplied with a muting-instructing signal (hereinafter referred to as "muting signal terminal") through a muting switch. Where the muting switch is closed and the FET gate is supplied with a muting-instructing signal (hereinafter referred to as "muting signal"), then the FET is rendered conducting. As a result, signals are prevented from being generated from the amplifier output terminal. One reason why the FET is applied is that this type of transistor shows a bidirectional characteristic between the source and drain regions and can be rendered conducting even with respect to signal components having both positive and negative polarities. Another reason for the acceptance of the FET is that it has a far higher linearity of characteristic than the ordinary transistor. In some cases, the FET is connected in series to the input side of the amplifier. However, the conventional amplifier using the FET presents difficulties in being assembled with the muting circuit in a single integrated circuit. Further drawback of the conventional amplifier is that since the amplifier itself is always rendered conducting regardless of whether the muting circuit is or is not actuated, switching noises arising when the FET switch is closed are transmitted to the output terminal of the amplifier.